The present invention relates to an apparatus for electrically testing electronic chip parts, commonly known as a devices under test (DUT), such as semiconductor bare chips before packaging them into devices, and, more particularly, to a quick disconnect articulated chuck located on the robotic arm which is used to transfer the chip parts from carrier boats to an electrical probe head of a chip tester.
A vital step in manufacturing electronic chips is testing the completed chips. This testing is typically accomplished by robotic chip handlers wherein the chips are plugged into a test socket, tested and then removed from the test socket, all automatically. Thereafter, the handler sorts the chips according the information obtained in the testing sequence that it receives from the computer making the tests.
In a typical test, a number of chips to be tested are placed on carrier boats which are moved through one or more preconditioning steps, a test step, and optional post conditioning steps. The preconditioning steps generally involve bringing the chip to the test temperature. Following preconditioning, the chip in the test step is positioned so as to be engaged by a chip nest plate on a robotic handler arm. The chip nest aligns with test contactor pins on the electrical test station for contact with the pins of each chip to be tested for supplying and receiving the test signals from the device.
As chips have become more intricate and as chip geometries have shrunk in recent years, the task of handling these chips and aligning the chips for electrical test has become more demanding. At the same time, it is common practice to operate the automatic testers essentially continuously. The two principal problems are in assuring a proper alignment between the chip and the contactor pins for every device, and to perform this task in a manner that reduces mechanical wear on the device handling and testing components. To the extent that there is wear, it is desirable to minimize the disruption to the testing operation by providing a quick disconnect capability for the components most likely to require replacement. The objectives of the current invention include providing an articulated chuck for improving the alignment of the test components, and to provide a quick-disconnect capability for that chuck to permit rapid substitution for that part to minimize production downtime.
An exemplary chip tester comprises a compartment for holding a plurality of chip carrier boats at temperature. Typically, the four robotic arms of the chip tester each obtain one or two chips at a time from the boats and hold those chips in place as the arms rotate 90 degrees to present those chips to respective electrical test stations. The robotic arms typically include a chuck assembly which is designed to provide a vacuum to hold the chip or chips in place during transport and testing. The chuck assembly also assists in the alignment of the chips to the electrical test station.
In prior art, alignment was typically obtained by a combination of alignment pins and bushings between the chuck assembly and the electrical test head, and final alignment was obtained by forcing the chuck assembly to mate with the electrical test head. In high speed, repetitive, testing operations, this alignment scheme resulted in accelerated wear of the chuck assembly and in relatively high rates of test misalignment and in damaged chips and equipment. The replacement of the chuck assembly required a partial disassembly of the robotic head to access the part. In the current invention, wear is substantially reduced by improving the alignment between the chuck assembly and the electrical test head, the required alignment mating forces are reduced, testing efficiency is improved, chuck replacement time is substantially reduced, and the chuck may be replaced without disassembling the robotic arm mechanism.
The prior art includes references to chip guides for positioning the chip onto the stage of test device. U.S. Pat. No. 5,561,386 issued Oct. 1, 1996 to Funaki, et al entitled xe2x80x9cChip tester with improvements in handling efficiency and measurement precisionxe2x80x9d describes a chip tester including a chip guide.
U.S. Pat. No. 5,828,223 entitled xe2x80x9cUniversal chip tester interface devicexe2x80x9d issued Oct. 27, 1998 to Rabkin et al. describes a robotic test machine for testing chips including a novel interface between the chips being tested and the plunger head loadboard which permits rapid changes of products being tested.
U.S. Pat. No. 5,192,908 entitled xe2x80x9cSemiconductor device testing apparatus with positioning mechanismxe2x80x9d issued Mar. 9, 1993 to Shibata describes a fourchucking-position electrical test apparatus.
The current invention relates to an improved quick disconnect articulated chuck which may be easily removed from the robotic drive mechanism for service. A real advantage is obtained by enabling a quick change over, resulting in a cost savings both in labor required for maintenance and in reduced production downtime.
It is another object of the invention to provide a quick disconnect capability while improving the accuracy of the chuck.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices, and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
In a typical electronic test environment, a robotic test machine is used to remove individual chips from a boat and to place each chip in the position that can be probed in an electrical test. This test may be conducted at the ambient temperature, or at reduced or elevated temperature in a controlled environment.
In order to use standard test equipment for a variety of chip geometries, special tooling in the form of a chuck which supports various chip nests is typically used to support various chip sizes in alignment with electrical test machine. When a device is changed, its unique chip nest is typically placed at the end of the chuck. In the current invention, a rigid chuck is replaced by a quick-disconnect articulated chuck which connects the chip nest to the robotic shaft in a manner that provides alignment accuracy, flexibility, and a vacuum attachment means to assistant capturing and containing the chip. The chuck supports the various chip nests which are typically unique for each size of chip.
The robotic test machines are subject high usage rates, in there is often a need for maintenance or replacement of the tooling. Typically, it is necessary to remove the plunger head in order to access the chuck. It is also frequently necessary to remove portions of the robotic support arm, including support springs, in order to disassemble a conventional chuck. An objective of the present invention is to provide a novel design wherein the chuck may be removed quickly without removing the plunger head. Since the chuck is often difficult to access, the quick disconnect capability provides significant labor savings and production downtime avoidance.
The preferred embodiment of the chuck is comprised of a chuck base housing which typically remains attached to the robotic arm; and a quick disconnect assembly. The quick disconnect assembly includes a vacuum sealing means, a retractable piston with vacuum cup attachment for securing a chip, a plunger head, alignment pins, and accessible captive disconnect screws. The base housing is mounted in a manner that permits articulation of the chuck to allow the chuck to obtain better alignment with the electrical test fixture; and a vacuum introduction means.
In an alternate embodiment, which is designed to permit a low-force alignment before substantial mating forces are applied between the chuck and a test fixture, a roller ball and detent mechanism featuring a mechanical home position is employed. The roller balls permit relatively low forces of the initial mating action between the chuck and the fixture to move the chuck into a position of better alignment, and therefore lower stress and wear. This initial movement is parallel to the plane of the test fixture to minimize binding of the chuck.
In alternative embodiments, the chuck may be a single piece improved parallel articulating chuck, or a simplified one-piece quick disconnect chuck.